A “Through‐Shell” Binding Isotope Effect

Small, but very significant: Partial separation of two hemicarceplexes which differed only in the degree of guest deuteration could be achieved by normal-phase chromatography (see picture). The difference in retention time arises from a variation in the interaction between the hemicarceplex and the silica surface as a consequence of a 0.005-Å difference in the CH and CD bond lengths of the guest molecules.